In a manufacturing process of semiconductor devices or flat panel displays (FPDs), a plasma is used to perform a micro-processing, such as etching, deposition, oxidation, sputtering or the like, so as to obtain a good reaction of a processing gas at a relatively low temperature. Conventionally, a capacitively coupled type plasma apparatus has been widely employed as a single-wafer plasma processing apparatus, especially, as a single-wafer plasma etching apparatus.
Generally, in the capacitively coupled plasma processing apparatus, an upper electrode and a lower electrode are disposed to face each other in parallel in a vacuum processing chamber, a substrate to be processed (a semiconductor wafer, a glass substrate or the like) is mounted on the upper electrode, and a high frequency power is applied to either one of the upper and the lower electrode. Electrons are accelerated by an electric field formed by the high frequency power to collide with a processing gas. As a result of ionization by the collision between the electrons and the processing gas, a plasma is generated, and a desired microprocessing (for example, etching) is performed on the surface of the substrate by radicals or ions in the plasma.
With a recent trend of miniaturization of design rules for the manufacturing process, a high-density plasma is required to be available at a low pressure for a plasma processing, and the aforementioned capacitively coupled plasma processing apparatus uses a high frequency in a frequency range (40 MHz or greater) much higher than a conventional frequency level (13.56 MHz, in general). However, if a frequency of a high frequency discharge is high, a high frequency power applied from a high frequency power supply to a rear surface or a backside surface of an electrode via a power supply rod is made to propagate to an electrode main surface (which faces a plasma) by a skin effect, whereby a high frequency current is made to flow on the electrode main surface from an edge portion toward a central portion thereof. Accordingly, an electric field intensity at the central portion of the electrode main surface becomes higher than that at the edge portion thereof, so that a density of a plasma generated at the central portion of the electrode becomes greater than that at the edge portion thereof. As a result, there occurs a problem that process characteristics become nonuniform in a radial direction.
To solve the problem, there have been made many researches including one that proposes forming flowerpot-shaped or tapered recesses on a main surface of an electrode to which a high frequency power is applied and burying a dielectric material in the recesses (see, for example, Japanese Patent Laid-open Publication No. 2004-363552 and U.S. Patent Application Publication No. 2005-276928). In such a configuration of the electrode, an impedance of a central portion of the electrode is greater than that of a plasma side, while an impedance of an edge portion of the electrode is smaller than that of the plasma side. Accordingly, a high frequency electric field at the edge portion of the electrode becomes increased, while that at the central portion of the electrode is weakened. As a result, the aforementioned nonuniform distributions of electric field intensity and plasma density can be ameliorated. Further, there has been also proposed an electrode structure with a high-resistance member disposed at a central portion of the electrode, but this structure results in an increase of power consumption due to a Joule heat (see, for example, Japanese Patent Laid-open Publication No. 2000-323456 and U.S. Patent Application Publication No. 2005-61445).
Meanwhile, as for the capacitively coupled plasma processing apparatus, a type that applies dual frequency powers to a lower electrode supporting a target substrate thereon is mainly used in recent years to optimize a plasma density and a selectivity of anisotropic etching individually. In the apparatus of this type, a first high frequency power of a comparatively high frequency (27 MHz or greater in general) suitable for plasma generation and a second high frequency of a comparatively low frequency (13.56 MHz or less in general) suitable for ion attraction are applied to the lower electrode concurrently (see, for example, Japanese Patent Laid-open Publication No. 2000-156370 and U.S. Pat. No. 6,642,149).
In the conventional plasma processing apparatus wherein two high frequency powers are applied to the lower electrode, in case the apparatus uses a high frequency range (40 MHz or greater) for plasma generation and employs the lower electrode structure in which the impedance of the central portion of the electrode is set to be relatively higher than that at the edge portion thereof by burying a dielectric material or a high-resistance member as described above, a uniformity of an electric field intensity distribution on the main surface (top surface) of the lower electrode improves for the high frequency power of the high frequency for plasma generation. However, for the high frequency power of the low frequency for ion attraction, an electric field intensity at the central portion of the lower electrode becomes lower than that at the edge portion thereof, which results in a deterioration of the uniformity of the electric field intensity distribution. Thus, there is a trade-off problem that a uniformity of anisotropic etching accuracy is deteriorated while the uniformity of the plasma density can be improved.